The intestinal mucosa is continuously exposed to a myriad of antigenic, mitogenic, mutagenic, and toxic stimuli. Under normal conditions the mucosa is maintained in a state of immune tolerance posing no risk to the well being of the organism. The intestinal LPT is largely responsible for establishing and maintaining this state of "physiological inflammation". Yet LPT are capable of responding vigorously and effectively to stimuli resulting from a pathological process. Hence LPT have the ability to toggle between hyporesponsive tolerant cells and fully activated effector cells. Recent advances in cell biology and signal transduction have introduced the concept that the plasma membrane contains heterogeneous lateral lipid assemblies composed of sphingolipids and cholesterol, termed lipid rafts, which serve as discrete microdomains for the enrichment of many proteins. Within a T cell it appears that these lipid rafts act as "gatekeepers of signal transduction". Functional T cell responses initiated through the antigen-specific T cell receptor (TCR) require the integrity and aggregation of these lipid rafts. We have developed an in vitro model to study the regulation of immune tolerance in mucosal human LPT. We have shown that freshly isolated LPT are hyporesponsive for proliferation, cytokine production, and membrane proximal tyrosine phosphorylation events when stimulated through the TCR/CD3 complex. In striking contrast to peripheral blood T cells (PBT), which are activated via the CD3 pathway, LPT responses are dominated by an alternate pathway, which uses the CD2 receptor. In addition, these LPT can be "re-programmed" with interleukin-2 (IL-2) to reacquire the ability to signal effectively through the TCR/CD3 complex, proliferate, and secrete cytokines. We have confirmed the presence of lipid rafts in LPT and have observed heterogeneity in the glycolipid and protein composition between rafts in LPT and PBT, and within LPT between proteins known to transduce a signal from the TCR/CD3 complex, leading to the following central hypothesis: Mucosal T cell tolerance is maintained by the differential targeting to discrete lipid rafts of proteins that regulate T cell activation via the CD3 and CD2 receptors. Our aims are: (1) contrast the membrane partitioning of proteins involved in proximal signaling events after activation through the CD3 receptor in freshly isolated, non-responsive LPT with responsive LPT; and (2) investigate the association of CD2 and its membrane proximal signaling cascade, with lipid rafts. It is anticipated that this unique approach will generate important new information on intestinal immune tolerance by examining the regulation of membrane proximal events in LPT signaling and how these modulate mucosal T cell mediated immunity.